Linux: adapt to truncate sequence changes

Linux: adapt to truncate sequence changes

As part of changes to the truncate sequence, inode_setattr() no
longer exists, and all filesystems have to define the setattr op
so we can assume that it is not NULL.

Introduce a compat inline function afs_inode_setattr that hides
the tests and the different versions from the main code.

Note that the existing test for the inode_setattr() return type
will fail, but the value is no longer used in that case.

This is required for 2.6.36

Reviewed-on: http://gerrit.openafs.org/2543
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry-picked from commit eaf3378f537935f6b9843886b43d)

Reviewed-on: http://gerrit.openafs.org/2550
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 58e56d080b8d19117b60f04ecb37af0c6dcafc1a)

Change-Id: I4cfdd191c60d7672c80aa3b3789e52c3e5e87666
Reviewed-on: http://gerrit.openafs.org/3519
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>